Nitration of saturated aliphatic



Patented Sept. 2, 1952 UNITED STATES PATENT QFFICEIjQ NITRATION OF SATURATED ALIPHATIC p HYDROCARBON S Henry B. Hass, Forest Hills, N. Y., and Lloyd G.

Alexander, Novman, -kIa., assignors to Purdue Research Foundation, La Fayette, 11141;, a corporation of Indiana No Drawing. Application May 26, 1951,

Serial No. 228,537

oxides of nitrogen, and the like, inthe presence of regulated amounts of molecular oxygen. Numerous e'iiorts have been made in the past to develop a satisfactory method of obtaining 1O nitro alkanes. Themost'efiective previously disclosed processes are those of Hass et al. described in U. S. Patent Nos. 1,967,667, 2,071,122, and

' 2,206,813, pertaining to the vapor phase nitration of paraffin hydrocarbons such as ethane,-"

propane, butane," and the like, by means of nitric acid or nitrogen dioxide, and that of Landon, de-

scribed in U. S. Patent No. 2,161,475, pertaining to the nitration of methane by'means of nitric 2 1 acid. i 1

All of the prior art processes are opento a number of serious objections, one of the most important of which has been the low conversions and yields of productsobtained based onthe 'nitric acid used in the process.- Becauseof itsc cost, corrosiveness, and the like, it is highly desirable to use as small a quantity of nitric acid as possible. jWe havenow discovered that the conversion of nitric acidto nitro alkanes as well as the production of valuable oxidation productsagig when parafiin hydrocarbons are nitrated in the vapor phase can be materially increased by effecting the vapor phase nitration of the hydro carbons in the presence of molecular oxygen in regulated amounts under certain restricted con- Z ditions of time and temperature. This is accomplished by the introduction of the oxygen in "such a way as to cause consecutive or simul- 'taneous reaction of the hydrocarbons with oxygen and the nitrating agent. 1,40

The use of oxygen in the manufacture of nitro alkanes by'the vapor phase nitration of paraflin hydrocarbons" has been generally referred to in the Hass et a1. U. S. Patent No. 1,967,667, referred to above, wherein discussing various methods whereby the yield may ossibly be increased, they say if desired, air or oxygen may be mixed with the hydrocarbons (such as iso butane), in order to reoxidize the oxides of'nitrogen to nitric acid; but if this is done, care must be taken to avoid explosive proportions." No further directions or details, however, are given. That thedisclosure of this patent is obviously different from our present invention evident from aconsideration I of the following facts." It the quoted "statement 11 Claims. (01. 260-644) is interpreted to mean that theimprovement in yield is effected by the addition of the oxygen or air and carrying out the procedure in such a manner as to oxidize the oxides of nitrogen to nitric acid and thereby increase the percent conversion to nitro alkanes on the basis of the total amount of nitric acid consumed, it is obvious thatuthe oxidation of the oxides of nitrogen to nitric 'acid must be'carried out under conditions different from those disclosed in the cited patent for'the conversion of'the saturated aliphatic hydrocarbons to nitro alkanes. Calculations based on the data of Bodenstein (Zeitschrift 1 fur Phys'i'k.

Chem., 100, 68 (1922)sh0W that at 420 Cr, the approximate nitration temperature'used by applicants; with a nitric oxide content-of 5 per cent and an oxygen content of'20 per cent; the oxida- -tion of the nitric oxide would be less than 3 per cent complete in 1.5 seconds. 0 conversion would be much less. than this because Actually,-- the the average percentages of 'nitric'oxides and oxygen in the reactor would be much'less thanthose assumed. A low temperature and atlong 'c'ontact time of the order of several hundredseconds would be necessary toefiect substantialoxidation of thenitric oxide. '1

If, on the other hand, it is assumed that the above-cited statement means that some undetermined'amount of oxygen is added to the reaction mixture of the type disclosed in the specification of the cited patent and that the nitration reaction is then carried out as disclosed therein, the improved results claimed by applicants will not be obtained and,'as a matter of fact; the addition of oxygen to the reaction mixtureoften leads to drasticallyreduced conversions; The cited patent mentioned a mole ratio of hydrocarbon to nitric acid of2 to 1 (a weightiratio, in the case of isobutaneoi 1.84 to 1). In thause of oxygen according to applicants"claimedprocess in order to give increased conversions ofthe nitrating agent to nitro alkanes; considerably higher weight ratios of hydrocarbons to nitrating agents are necessary, i.'e., ofthe order of from 8 to 25 moles of hydrocarbon per moleof nitrating agent; The improved process whereby we obtain increased conversions and yields of both nitrolalkanes and oxidation products such asa'lcohols. aldehydes, acids, etc. consists essentially in conducting the vapor phase nitration of saturated aliphatic hydrocarbons at temperatures ranging from'250" C.- to 550 C. Witha nitrating agent such as nitric acid inthe presence of molecular oxygemthe hydrocarbon being used inajproporcreased (space velocity increased), or both of these changes may be made simultaneously.-

Since it is usually desirable to operate at constant space velocity, it is most convenient mere- 5 to 40-;.-per centlby ,volume of the hydrocarbon 5/ -1y to;adjust;;the reaction temperature in accordused. sgBykcarryin'g outthe nitration under, such conditions the conversions to nitro alkanes, based on nitric acid, are increased by as much as 100% over the conventional method of nitration in the r ,iancewit-lnthe aciditybf :the aqueous *layer. Very 7 small adjustments in temperature will cause rel- -.atively large fluctuations of the acidity, and the temperature adjustments should therefore be absence of oxygen. Such increases in-conversions lo irmade, gradually. The acidity of the aqueous layer and yields permit the production of nitro'alkanes at materially lower:costs: because" of increases in plant capacity,:,10.werrram-material cost,and lower labor costs}: '-.Itiis obviousg-there "of the product (expressed in normality), should rnraorder: to :obtain best results. The optimum t withinithisirange,in any given case, will depend fore, that even relatively low increases in con- 15 upon' the particular alkane being nitrated, and

versions are of great importance, inetheproduction of relatively expensive materials 'sfuchg as the nitro alkanes.

Our process is, in general, applicable to the nitration of saturated --I aliphatic hydrocarbons AI centainlnga fromi -I l to l 4 .a carbon, atoms; such 'as amethanas:ethaneri-propane; butaneg-and isobutane..

,. Qur: proeesscmay 2be 1satisfactorily:carriedgout ;.l=;depending.lupon. the hydrocarbons; being ni- I rated; the:products desired, .aandirothertjcondii;-tions::; :However-,: the reaction timermustbe, ala terediinz-accordance.with the temperature used,

a, on the composition of the reaction mixture. This general procedure is more completely disclosed in U. S. Patent No. 2,327,964 by Edward B. Hodge, granted August 24, 194 3.

The amount of molecular oxygen used in our --:process, .isrdeterminedr by:'severalinonsiderations. In z-the' -.:first;place;z:.care :must; be;- takenj avoid :;exp 1osive: proportions; In the 'secondz l ce, the -:'use;':0f;: toozlargea"; proportion of oxy en:- may ovenamide-temperaturerange, say..250 C;-'to' 550 cause ;the;.:liberati0n:of amexcessiveramounti of ,qheatz-iand thus: lead to lowered;:conversions throu h lack, oi.-- adequatetemperature control.

Since,howeventhelatter faQb Ii S affected-som -.:what.aby.:thereactor-design; it isgobvious: that the es'ubstantially longerzi-tiineabeing'zrequired;for.:the' aoramount Qty-molecular 9Xy enjwhich cambemsed --lower;temperatures sand, in general the higher eithezztemperatureremployed,:. the shorter will-.- be ,i'lthea contact ztimee-for." optimum conversion of efdtric acid tosnitro alkanes... In general', the con- 7 depends towsome extentaun n k d; of; equ pmentxused'. :=;A1S0,-.,the:. S ZOf, a: larger proportion of hydrocarbon"in,generaL-givess betterttemperatune: control a-nd-,-. thusl permitsethe use ofiglarger,

-rtactj-timesused-whenmolecular oxygenis present 35. rnmpo t ons "of1zpxygeninwe haveg generally round :1 that thequseof anaamount of. oxy en quivalent to 5 mic-p rcentr r-volumepi e-.h d zo rhon si sedr y s mo tzsatisfiactqryar ul s1 te i w h s -rx H wev r-e we-shevez gun 'spaceivelocityamkregulated inthesamgeneral 40 upper limit to the increase of conversion afi l manner a's in the-prior art processes.

Hme moIecuIar-J oxygen-used in 1 our process may w added -either as substantially-pure oxygen or ':as air= containingi an equivalent amount of-oxyaz 'gen'u other oxygen-containing gases :may also- -covery of thedesired products fromthe reactionglio mixture. W I r The optimum time of contact for a given reaction=-temperature can most-con eniently bev-determined for a given-reaction mixture by regulatane-trauma of-conta'ct for the reaction mixture 1.55 3 i3 0; $91 C beio gddipee tr e-agld- 'at' the -selected reaction temperature so asto maintain the acidity; of the reaction products "tvithir'r-a' relativelyfinarrow range Since water is '-bne"of the reaction products-of the-nitration rei' afetiom-and the nitro-alka'nes'are in' all-casesatiflo in the examples givensbelow,

le'ast partially immiscible with Water; the liquid auction-productsseparate into two. layers'.-iThe j'titratable acidity o'fthe aqueous layer constitutes ?'a convenient measure of theaciditv of thereacproport 0 @Qxr n ;v ra r owa d' he mexplcs verlim t ;:"I? r re:processr Qt i n s re m a im rwe r methe co cep Q rexarn ples oxygen may-;- be adde carbo :before or tenthe intro A v ii eci ;se er' ;3 1 1 1 18 h ug mediana eousw v *QivepQ iz lthe-n t q eidriil :mix-mm or s e e dsiat tsmpsra weao The.fconcen rationsgor"the nitr' cid-use n :bewar edmeramideman e wi t;n et afieeting themsults; 135%: nitric aci -hav n 5 en equallyas;go9d;resultsasth i'l %rn ;hf: q ci e A1though:we;.p1tefen:to iu'semitric "acid vapor as xthezzznitrat n r agentr 1115; Q t3p TQQ i nitm en rdioxide'mayz -lsosberused:andaox en exerts the same beneficial ,iefrectrwhen employed with {this tionproducts, and-this -value may be used as az365 in-iti'atingczag ent; :Inazgeneralitheaconditions jor basis for the control of the time-temperature ac- "torijlIfthe-acidity of the aqueous layerof the reaction products'rises above the-desired-operat- "ing range, the reaction temperature should be i,using;:'nitrogen; r-fdioxide; in CD111:SII'OCBSSFQYfi'thE 's'ame:as those employectwhen:nitriczaacid :is used. However, :lthe :conversions of mtro'gemdioxidefto gnitrozalkanes are;:somewhatilowerrthanithoseaob- ,increased, or the contact timeincreased:(space ::tained kwithsnitriczacidaunderzianalogous econdi- 'bedecrea'sed', or the"contact time -should beidelimximon5113 1 1 mean m-1 23 3 :-tions.'-;" z: a H 4 tzrAsaplielkiolisly indicated, our process'give grise snot ionly togincreased conversions: and; ields 9 znitmialkanesabutialso;to'vipcreased f n tip of used. The'increased amountsiofthese oxidation products represent one of the valuable advantages of ourflprocess in view of the fact that it gives rise to the 'formation of sufficient products of this character to justifytheir recovery from the water soluble fraction of the nitration reaction. Among these oxidation products may be mentioned formaldehyde (from methane) and formaldehyde and acetaldehyde from higher hydrocarbons; The amount of these aldehydes are substantially increased by the use of oxygen. Other valuable oxidation product such as alcohols and acids arealsoformed.

Ourv process will be illustrated by the following examples: Y r v EXAMPLEI- A reactionmix'ture consisting of 8 moles of propane and" 1 mole of67.0% nitric acid was passed in thevapor phase through a reactor consisting of a forty foot coil of Pyrex glass tubing (7 mm. diameter) immersed in a fused salt bath at a temperature of 425 0., the contact time being about 1.5 seconds. The addition of oxygen to the propane-nitric acid reaction mixture in varying proportions caused increases in conversions as shown in the table below.

Table I Oxygen in Conversion of Formaldehyde Propane oxy- Nitric Acid to Produced per gen Mixture; N itro Alkanes, Gram of N itro Percent Percent Alkane, grams Other water soluble oxidation products were also present.

EXANIPLE II Ethane was nitrated with nitric acid in the vapor phase in the same reactor described in Example I. The molecular ratio of ethane to nitric acid was 12 to 1. The salt bath temperature was 430 C. and the contact time was about 1.5 seconds. The addition of oxygen caused an increase in conversion of nitric acid to nitro alkanes as Methane wasnitrated with nitric acid in the vapor phase in an apparatus of the type described in Example I at a temperature of 435 C. and a contact time of about 1.7 seconds. The molecular ratio of methane to nitric acid was about 15 to 1. The conversion of nitric acid to nitromethane was increased from 17.6% to 24.2% by the addition of oxygen when the oxygen content of the methaneoxygen mixture was 15%.

nitrogen dioxide in an apparatus of the type described in Example I, the temperature of the salt bath being 410 c. and the contact'time about 1.7 seconds. The molecular ratio of hydrocarbon to nitrogen dioxide was about 10 to. 1. Addition of 3.1 moles of oxygen per mole of nitrogen dioxide increased the conversion to nitro alkanes from about 14% to about 25%. H 1

l The efiect of variations in temperature and proportions of oxygen used in the nitration of propane are further exemplified in Table III which follows. It willbe noted'that in experiment No. 46 reported in this table the oxygen used was introduced in the'form of air. I

Table III Expt. No 30 33 46 35 37 39 Temp. C 410' 410 410 410 395 395 Pressure, mm. Hg. 970 990 990 990 970 960 Contact time, sec 1.6 1.6 1.6 1. 6 1. 6 .1. 6 Cone. HN03. 69.0 69.0 69.5 69. 0 69. 5 69. 5 Moles CaHs/mole HNOa-.. 11.1 10.9 9. 5 10. 4. 11.0 11. 4 Moles 0 /mole HNOs 0.0 0.9 2 2. 0 3. 5 0.0 3. 8 Volume ratio 1 1.0 0.89 0.90 0.80 0.97 0.70 Gonv. to nitro alkane cent 28. 1 49. O f15. 0 62. 1 19.5 76. 0

1 Ratio of the exit gas volume to the inlet gas volume.

2 As air. r

The useof oxygen in the vapor phase nitration process not only afiects the conversionsbut also the ratios of the amounts ofthe variousnitro alkanes produced. This is illustrated in Table IV. below, showing the nitration of propane.

Table IV a Conver- Experiment number 31 35 sion', 2 l I R o. 1

Moles Oz/IDOIB HNO: O. 0 3. 5 Conversions, mole percent:

Nitromethane, percent 3.8 17.9 4.7 Nitroethane, percent 5. 7 10.7 1.9 Z-Nitropropane, percent. 7. 8 14.1 1. 8 l-Nitropropaue, percent... 11.1 19.5 1. 7 Total Conversion, percent.. 28. 4 62. 1 2. 2 Composition of product, mole perc Nitromethane, percent... 13.2 .28.8 Nitroethane, percent 20. l 17. 2 Z-Nitropropane, percent. 27. 5 22. 6 l-Nitropropane, percent 39. 2 31. 4

It is to be understood, of course, that we are not limited to the specific operating procedures set forth in the above specific examples since various modifications of the procedure set forth therein will naturally occur to those skilled in the art. For example, the process may be operated in a cyclic manner if desired. Various methods of bringing the reacting gases to the desired reaction temperature may be employed. More dilute solutions of nitric acid than those shown in the specific examples may also be used. The reaction may be carried out at more elevated pressures than those shown. Still other variations common to the prior art may be employed and it is distinctly understood that we may so vary our claimed invention so long as the particular improvement hereinabove disclosed and covered by the appended claims is followed.

This application is acontinuation-in-part of our copending application Serial No. 15,504 filed March 17, 1948, now abandoned.

Now having disclosed our invention, what we claim is:

1. In a process for the production of improved yields of nitro alkanes and oxidation products of parafiin hydrocarbons by the vapor phase nitraanswer titles; Qxy Qn-;..-with=' anaturated aliphatic-hydro? arlmmcentaining3irom- :1 tori carbon atoms. and a'amaterialselectemfrom the groupeconsisting. of

"nitric .acid;and nitrogendioxide, said. hydrocarbon and said .nitrating agent being .in a. molar ratio ranging from 8 to 1 to 25 to-v1:cand .maintaining said mixtureatrsaid elevatedtemperatures for a suflicient. period of time topermit substantial nitrationofith hydrocarbons butnot substantial oxidation of nitrieoxide to nitrogen dioxide.

' 2; EThe ,processiofclaim 1 wherein-the elevated temperature ranges froma25fifl C-:- to 550 C.

3. The process of clairn -l; wherein the molecular V .gx scn snresent to theextent of five to .forty per cent by .volurpe oi, the said saturated aliphatic elevated temperatures-oxygen, with propane and nitric acid said propanetandigsaid nitrating agent being vin avmole ratio ranging from 8 to 1 to 25 to 1 and inaintaining said mixture at said elevated temperatures for a sufficient period of time to per- 313' bstanti l ritretien cities 'parafiin, bu not substantial-mxidation pfinitric'ic idei-tonltregen dioxide. L, :11 21: r :f 7.1!1 heprocess of claim 6. swh'ereingthe -molecuiaass oxygen is presenttoathe ee'xtentof flveito iorty per cent-by volume o fivthe saidlpropane. a. 8. Theprocess-ofi claim fi-swherein the :elevated temperature ranges fro'm 2508 to 550" C. .9; The process of claim: 6 wherein'the- -elevated temperatureiranges ar ifrom 250 C; to:v-'550 C;,

the oxygen is present-to theext'ent 01 5 to-40%1by' volumeon-the-said propane; and thesaidreactwn mixtureismaintainedaat said reaction tempera-j ture for a regulated peridof tiinesuch that tne aqueous-reaction products' haye anacidity gwithin the range between oil}! and l.5 N. 10. The process -or claim--6 -wh d t v The followinggreierences are-gfi record =in -"the file of this-patent: r v UNITED STATES- PATENTS Number Name Date 66 Hes -.J- i y-2 1934 2,190 453 Kin Feb-4'3. 1940 2,327,964 Hodge N ug; 24 194s Hass; Ind;; and Eng. Chemistry, vol. 28 1936), pp. 339944., I 

1. IN A PROCESS FOR THE PRODUCTION OF IMPROVED YIELDS OF NITRO ALKANES AND OXIDATION PRODUCTS OF PARAFFIN HYDROCARBONS BY THE VAPOR PHASE NITRATION OF SATURATED ALIPHATIC HYDROCARBONS CONTAINING FROM 1 TO 4 CARBON ATOMS, THE IMPROVEMENT WHICH COMPRISES CONTACTING AT ELEVATED TEMPERATURES, OXYGEN, WITH A SATURATED ALIPHATIC HYDROCARBON CONTAINING FROM 1 TO 4 CARBON ATOMS AND A MATERIAL SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID AND NITROGEN DIOXIDE SAID HYDROCARBON AND SAID NITRATING AGENT BEING IN A MOLAR RATIO RANGING FROM 8 TO 1 TO 25 TO 1 AND MAINTAINING SAID MIXTURE AT SAID ELEVATED TEMPERATURES FOR A SUFFICIENT PERIOD OF TIME TO PERMIT SUBSTANTIAL NITRATION OF THE HYDROCARBONS BUT NOT SUBSTANTIAL OXIDATION OF NITRIC OXIDE TO NITROGEN DIOXIDE. 